Wafer-thin starlets are always bragging in interviews about how they can eat anything they want because of their "high metabolism." But it's more likely they're on one of the many trendy diet plans that flow through Hollywood.

We're taking a look at the latest crop of celebrity health food fads, and seeing how they really measure up.

PALEO DIET

Star followers: Megan Fox is rumoured to be following it.

What it entails: Based on the same eating habits and principles of our hunter-gatherer ancestors, the Paleo diet involves eating grass-fed, pasture-raised meat, fish, vegetables, fruit, roots and nuts, and avoiding foods our ancestors had no access to, such as grains, legumes, dairy products, salt, refined sugar and processed oils.

The expert's take: "If everyone ate this way, we'd probably see a 50-to 80-per cent drop in Type 2 diabetes and obesity," says Kyle Byron, a nutritionist and personal trainer who works with pro athletes. "It's based on eating real food . . . No grains or dairy -- that's the hard part.

"The theory is that we were never meant to eat grains or dairy, so removing these things reduces chronic pain and disease, and increases fat loss/ healthy body. You do have to do a bit of cooking, though."

RAW-FOOD DIET

Star followers: Demi Moore and Martina Navratilova have both worked with Dr. Doug Graham, one of the founders of the raw-food movement.

What it entails: There are a lot of different ways to approach a raw food diet, but it's primarily made up of raw, unheated food (less than 46 C). Researchers believe cooking food will take away its nutritional value and ability to be best absorbed by the body.

The expert's take: "Another great concept," says Byron. "Cooking meat at high heat can make it carcinogenic.

"Cooking vegetables creates nutrient loss, and processed food might have chemicals that are bad for us, or leave us feeling like we want to eat more food," he adds.

VEGANISM

Star followers: Many stars have opted to side with PETA and adopt a vegan lifestyle. Celebrity proponents of the vegan diet include Alicia Silverstone, Ellen DeGeneres, Portia de Rossi and Sir Paul McCartney.

What it entails: Steering clear of any animal byproducts, including dairy.

The expert's take: "This is a plantbased diet and it can be controversial," says Byron.

"In my experience, some vegans are malnourished because they don't know enough about nutrition to see what they are missing, or they don't plan enough, so they end up eating a lot of bread and processed grains."

Byron suggests that, to make this diet more manageable and healthier, you should make sure you're getting enough vitamin B12, iron and calcium.

JUICE CLEANSE

Star followers: Gwyneth Paltrow, Beyonce

What it entails: The juice cleanse is a type of fasting that only lets you consume fruit and veggie juices. Liquid foods are digested easier and faster, resulting in spikes of serum glucose -- meaning your body doesn't burn as many calories as it would if you were eating a whole fruit or vegetable.

The expert's take: "[The juice diet] is low-fat, low-protein, high-sugar and it is likely to cause weight gain and leave you feeling hungry -- despite all the calories you can take in," says Byron.

"The sugar would cause weight gain and you would be left feeling hungry, because there is little protein and nearly no fat."

Byron suggests to "add protein powder and nuts to the juices, and try to reduce or eliminate the fruit."

SUNDOWNER

Star followers: Kate Beckinsale

What it entails: Not eating after a certain time (usually 6 p.m.), so no latenight snacks or pre-bed nibbling.

The expert's take: "If you have an active job or you exercise after work -- which more than half of exercisers do -- then you have to eat late," says Byron.

"Just limit it to protein to recover damaged tissue and promote metabolism, healthy carbs like fruits and vegetables to promote energy recovery, and micronutrients and fats for hormonal health and to help you feel full."

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